Reactance and Impedance

Reactance and Impedance

What is Reactance?

Reactance is essentially the inertia against the motion of electrons in an electrical circuit i.e. the attribute against the flow of electrons in an electrical circuit. It is denoted by the symbol R and is measured in units of the greek symbol ohm. In an electrical circuit, it is mathematically the ratio of the potential difference V and the current flows between two points in that circuit.

R = VI

It is also known as the imaginary resistance of an electrical circuit. The motion of electrons constitutes current generation in an electrical circuit and any inertia against this motion of electrons constitutes reactance. It is primarily generated due to the elements inductance or capacitance. In a magnetic field, it resists the change in current of the element whereas in an electric field resists the change in voltage of the element. It is mathematically represented by the letter X and has its unit of measurement in the form of the greek symbol ohm.

Types of Reactance

Reactance is primarily of two types:

  • Capacitive

  • Inductive

What is Impedance?

Impedance is a combination of resistance and reactance. It is essentially anything and everything that obstructs the flow of electrons within an electrical circuit. Hence it affects the generation of current through the electrical circuit. It is present in all the possible components of the circuit and across all possible electrical circuits. Impedance is mathematically symbolized by the letter Z and has its unit as ohm.It is a superset of both resistance and reactance combined.

In phasor terms, impedance Z is represented as a combination of resistance R and reactance X as:

X = R + j X

Where reactance X is a combination of Inductive  XL and capacitive Xc

X = XL + Xc.

Wattless Current

The component of the AC current that consumes zero power in a circuit is known as a wattless current. The average power dissipated in a AC circuit is given by the equation

P=VI cos ϕ

From this equation, we know that the average power dissipated not only depends on voltage and current but also on the cosine of the phase angle between them. In a circuit that contains only a capacitor or inductor, the phase difference between the voltage and current is π/2. Therefore, cosϕbecomes zero and the power dissipated will be zero. There will be no power dissipation in spite of the current flowing in the circuit. This current which results in no power dissipation is referred to as wattless current.

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Practise This Question

Which of the following option correctly defines wind?